// checkTitle can filter some options out, avoid empty sections
if ( count( $options ) > 0 ) {
$fields['TitlesNs' . $namespace] = [
- 'class' => 'EditWatchlistCheckboxSeriesField',
+ 'class' => EditWatchlistCheckboxSeriesField::class,
'options' => $options,
'section' => "ns$namespace",
];